Regulating system



June 21, 1949. 5. LE R. BRADLEY 2,473,854

REGULATING SYSTEM Filed Nov. 20, 1947 2b /2 /4 a7 44 3 22 L---4 54 M 2A8 loo ,1 Z

wnmzssss; INVENTOR Patented June 21, 1949 BEGULA'IING SYSTEM Schuyler LeRoy Bradley, Pittsburgh, Pa., aligns: to Westinghouse ElectricCorporation, East Pittsburgh, Pa a corporation of PennsylvaniaApplication November 20, 1947, Serial No. 787,123

20laims. 1

This invention relates to regulating system for dynamo-electricmachines. and in particular, to systems for maintaining minimumexcitation of such machines.

An object of this invention is to provide a static system responsive tothe excitation of a dynamo-electric machine for maintaining theexcitation of the dynamo-electric machine above a predetermined value.

Another object of this invention is to provide a regulating systemhaving a simple and sensitive static electrical circuit for insuringminimum excitation of the machine being regulated.

Other objects of this invention will become apparent from the followingdescription when taken in conjunction with the accompanying drawing, inwhich;

Figure l is a diagrammatic representation of a regulating systemembodying the teachings of this invention, and

Fig. 2 is a graph the curves of which represent the impedancecharacteristics of certain parts of the system shown in Pig. 1.

Referring to Fig. 1 of the drawing. this invention is illustrated withreference to a regulating system for a dynamo-electric machine Ill suchas a generator. The dynamo-electric machine it comprises the armaturewindings l2 connected to load conductors [4, II and it, and a fieldwinding 20 connected across the armature windings 22 of an exciter 24.The exciter 24 is provided with field windings 20 which are connected tobe energised in response to the operation of a regulating exciter 28. I

The regulating exciter II is of the self-energizing or "series tunedtype which normallyv operates along the linear part of its saturationcurve. The regulating exciter fl is provided with armature windings ill,a self-energizing field winding 32 and two control field windings 34 and30. As illustrated. the iield winding 26 of the exciter 24 is connectedthrough a resistor 31 and the self-energizing field winding 32 to oneside .of the armature windings II of the regulating exciter 28, theother terminal of the field winding 20 being connected to the other sideof the armature windings II. The series field winding 32 is employed fornormally supplying the excitation requirements of the exciter 28.

The control field winding 34 is disposed to be directionally energisedto either aid or oppose the excitation effect of the self-energizingseries field winding 32 in response to voltage changes on conductors I4,is and it. Thus, the control regulator it across the conductors l4 andIt. Any suitable voltage regulator 38 may be employed, it beingpreferred. however, to employ the regulator having a voltage referencenetwork as disclosed and claimed in Patent No. 2,428,566, issued October7, 1947 in the name of E. L. Harder, et al., and assigned to theassignee of this invention.

In accordance with this invention, the control field winding 36 isdisposed to be energized in one direction only, in response to apredetermined degree of excitation of the generator It. In order toobtain such results, a three-legged saturable core reactor 40 isemployed foraiding in the control of the energisation of the fieldwinding 36. The saturable core reactor 40 is provided with a directcurrent control winding 42 which is disposed to be connected across thearmature windings :2 of the exciter 14. a resistor 44 being provided inthe direct current control winding circuit for adjusting the degree ofenergization thereof. Thus, the winding 42 is energized in accordancewith the excitation of the generator it, as determined by the output ofthe exciter 24.

The saturable core reactor 4. is also provided with a pair ofalternating current windings 48 and 4| disposed on the outer legsthereof and connected in parallel circuit relation with one another tobe supplied from a source of alternating current represented by theterminals in and 52, an adjustable resistor 54 being connected in thesupply circuit for the alternating current windings 4t and 48, thepurpose of which will be explained more fully hereinafter.

As illustrated, a saturating reactor circuit is connected across theoutput terminals 56 and it of the saturable reactor 4| for controllingthe current flow in the control field winding 36 of the regulatingexciter 20. This circuit comprises a saturating reactor 80, a capacitor62 and a dry-type full wave rectifier 64 connected in series circuitwith one another and across the terminals 56 and 58, whereby the currentflow in such circuit is controlled by the voltage appearing across theterminals It and 5B. The control field winding 15 is connected acrossthe output terminals of the dry-type rectifier 64, an adjustableresistor as being connected in such output circuit for adjusting thedegree of energization of the winding 36. where desired. The saturatingreactor series circuit Just described has an impedance characteristiccurve as represented by curve It of Fig. 2 and which will be fieldwinding I4 is connected through a voltage as referred to hereinafter,such that for changes in 3 voltage up to a predetermined value acrossthe terminals It and N current does not how in such circuit, whereas,for voltage increases across the terminals I. and II above suchpredetermined value, the current fiow in the series circuit increasesquite rapidly.

In operation, assuming that the system is as shown and that thegenerator II is being operated to supply a given load, the excitation ofthe generator II is at a normal value with the regulating exciter 24eing perated to maintain such normal excitation. If for any reason theoperating condition should change so that there is a decrease in thevoltage across the load conductors l4 and It, then the voltage regulatorll operates in a well-known manner to eilect the energisation of thecontrol field winding 34 in a direction to aid the excitation efiect ofthe'selfenergizing field winding 82 of the regulating generator 24, andthereby increase its output with the result that the excitation of theexciter 24 is increased. Under such conditions, the increase in currentfiow through the field winding 2. of the generator ll effectivelyincreases the excitation of the generator II to increase the voltageacross conductors l4 and I. to a predetermined value which is to bemaintained.

Ii, on the other hand. the voltage change across load conductors l4 andII is an increase, then the voltage regulator 34 functions to energizethe control field winding 34 in a direction to tend to oppose theexcitation efi'ect oi the self-energizing field winding 42 to decreasethe output of the regulating exciter and thereby decrease the excitationof the exciter 24. Under such conditions, the current fiow through thefield winding 2010! the generator II is operated to return the voltageacross the conductors l4 and It to the predetermined value which is tobe maintained.

In the foregoing operation described with respect to the control of thecontrol field winding 34, the efi'ect oi the control field winding 36has been ignored. If during the normal operation of the system, theoutput of the exciter 24 increases with the result that the excitationof the generator It increases, the direct current fiow in the controlfield winding 42 of the saturable reactor 40 is increased, with theresult that the saturation of the three-legged reactor 40 is increased.As the impedance of the parallel connected alternating current windings46 and 44 is thus decreased, the current fiowingin such windingsincreases. As the current how to the alternating current windings 46 and48 increases, the current through the adjustable resistor 54 eilects alarger potential drop thereacross with the result that the potentialacross the output terminals I6 and 54 of the reactor is greatlydecreased. This is evident for the voltage across the output terminalsI6 and I4 is equal to the voltage input to the alternating currentwinding circuit across the terminals 50 and 52 minus the potential dropacross the adjustable resistor 54. Under such conditions, the voltageappearing across the output terminals 58 and 58 of the saturable corereactor 40 is insufiicient to effect more than a minor if any flow ofcurrent in the saturating'reactor series circuit, with the result thatvery little, if any, current flows in the control field winding 36.

If, on the other hand, however, the output of the exciter 24 andconsequently the excitation ofthe generator I decreases, then thecurrent flow in the direct current control winding 42 of the saturablecore reactor 40 is decreased with the result that the impedance of thealternating current windings 4' and 44 is increased, and the currentflow therethrough is decreased. As the current drawn by the alternatingcurrent windings 46 and 44 decreases, the potential drop across theadjustable resistor l4 decreases substantially proportional to themagnitude of the current therethrough, with the result that the voltageappearing across the output terminals 44 and II of the reactor 44increases. When this voltage increases to a value above a predeterminedvalue. depending upon the impedance of the saturating reactor circuit,further increases of voltage efiects a large increase in the currentfiow in the saturating reactor circuit, with the result that the currentfiow through the saturating reactor circuit efiects a large increase inthe current flowing through the control field winding 36.

Under such conditions, if the voltage regulator 30 is operating toenergize the control field winding 34' in a direction to oppose theexcitation efi'ect of the self-energizing field winding 32 to force theexcitation of the exciter 24 downwardly, then the current fiow throughthe control field winding 36 from the saturation core reactor circuitopposes the regulating effect of the control field winding 34 to tend toaid the excitation efiect of the self-energizing field winding 32 toincrease the excitation of the exciter 24 to maintain the output thereofat a value above a predetermined value to maintain a. predeterminedminimum excitation of the generator Iii.

As will be apparent when the current flow in the control field winding34 isof sufilcient magnitude tocounterbalance the excitation effect inthe one direction of the control field winding 84, then the control ofthe regulating exciter 28 is no longer dependent upon the operation ofthe voltage regulator 28, but-is dependent upon the functioning of thestatic circuit, including the saturable core reactor 40 and thesaturating reactor circuit connected thereacross. The saturating reactorcircuit and the adjustable. resistor B4 of the static circuit cooperateto give a very sensitive control of the energization of the con-, trolfield winding 30 in response to variations in the output of the exciter24, and consequently. the excitation of the generator l0.

While reference has been made hereinbei'ore with respect to thesensitivity of the minimum excitation system for controlling theexcitation of control field winding 88, this sensitivity and theoperation of the circuit will become more apparent by reference to Fig.2 of the drawing. In Fig. 2, curve CI is a representation of the volt:age output across the terminals 58 and II of the saturable core reactor4| as the alternating current input to the alternating current windingcircuit varies and curve II is a representation of the impedancecharacteristics of the saturating reactor circuit composed of the seriesconnected saturating reactor Ill, capacitor 82 and full-wave rectifier64. The shape of the curve 10 of course can be varied somewhat dependingupon the choice of the capacitor 62 and the saturating reactor 60.

As explained hereinbefore, the voltage across the output terminals 86and 88 of the saturable reactor 40 for any given energization of thedirect current control winding 42 is dependent upon the voltage input tothe energizing circuit of the parallel connected alternating-currentwindings 40 and 48 of the reactor 40 and the potential drop across theadjustable resistor 54.

amasse- 'lhusasthepotehtialdropacrossresistoruincreases, the voltageappearing across the output terminals it and I. decreases.

Referring to the curves I and II of Fig. 2, it is apparent that as thevoltage appearing across the output terminals it and it initiallyincreases to a predetermined value represented by the point 12, there isno current flowing in the saturating reactor circuit connected acrossthe output terminals I6 and It. At this point, current of small valuebegins to flow in the saturating reactor circuit and as the voltageacross the output terminals It and II of the saturable reactor 40increases, the current ilow in the saturating reactor circuit increasesuntil the voltage across terminals l6 and II increases to the point 14indicated on Fig. 2. It is thus seen that the current flow in thesaturating reactor circuit at first increases in small increments untilthe voltage indicated as at 14 appears across the output terminals atwhich point .the total current'fiow to the alternating-current windings48 and 4t and to the saturating reactor circuit is represented by theline between points 14 and I6 appearing on the drawing. Thus the currentin the alternating-current windings is represented by the line betweenpoints It and I6 and the current in the saturating reactor circuit isrepresented by the line between points 14 and II.

Now if the current flow in the alternating-current windings 48 and 48 isdecreased by reason of a decrease in the current flow in thedirectcurrent control winding 42, such a decrease in the current fiow inthe alternating current windings 46 and 48 tends to decrease thepotential drop across the adjustable resistor 54 with the result thatthe voltage appearing across the output terminals 56 and 88 tends toincrease. When the voltageacross the terminals 56 and 5! tends toincrease, the current now in the saturating reactor circuit isincreased. This results in a total current through the adjustableresistor 54 larger than that represented by the line between points 14and 16. Therefore, the potential drop across the adjustable resistor 54increases, thus decreasing the voltage appearing across the outputterminals 56 and 58.

As the current in the alternating current windings 46 and 48 continuesto decrease as a result of decreasing the direct current in the controlwinding 42, the voltage across the output terminals 56 and it continuesto attempt to rise but as a result of this tendency to rise, largermeasure of current flows through the saturating reactor circuit causingthe total current that flows through the adjustable resistor I4 toincrease. As a result of this increased current in resistor 54, thevoltage across terminals 56 and 58 decreases and follows along thecharacteristic curves 68 and 10. As the voltage follows along thecharacteristic curves 6! and 10, the current appearin betweencorresponding voltage P ints on the curves Ill and 68 is decreasedslightly, representing the decrease in current drawn by the alternatingcurrent windings 46 and 4!, whereas the current appearing betweencorresponding points on the voltage ordinate and the curve I. greatlyincreases repre-. senting the current flow in the saturating reactorcircuit and consequently in the control field winding 36. It is thusapparent that for slight changes in voltage across the exciter 24 a verysensitive control of the minimum excitation circuit is obtained giving alarge increase in current flow in the control field winding 36 for veryslight changes in voltage across the exciter 24 after the predeterminedvoltage output of the reactor 4|, as represented by the point I2referred to hereinbeiore is reached.

'I'he'system or this invention is very sensitive in operation,being'eiiective to maintain regulation of generator II and to insurethat the excitation thereof will not decrease below a predeterminedminimum value. As the minimum excitation clrcuit is formed of staticcomponents, it is apparent that the system will be quite stable duringoperation, gives a fast response and requires little maintenance. Thesystem is formed oi. standard components and can b readily duplicated byone skilled in the art.

I claim as my invention:

1. In a regulating system for a dynamo-electric machine disposed tosupply a load circuit, in combination, an exciter for controlling thefield excitation of the dynamo-electric machine, a main control fieldwinding for the exciter dispoud to be directionally energized to controlthe excitation of the exciter, means responsive to a change in conditionof the load circuit supplied by the dynamo-electric machine disposed foroperation to control the directional energization of the main controlfield winding, an auxiliary control field winding disposed to beenergised in one direction only in opposition to a predetermineddirectional energization of the main control field winding, and meansfor controlling the energization of the auxiliary control field winding,said means including a saturable core reactor having a direct-currentcontrol winding disposed to be energized in I accordance with theexcitation of the dynamoelectric machine, alternating current windingsfor the reactor connected to be supplied from a source of a1. .atingcurrent, a circuit including a saturating re I tor and a dry-typerectifier connected to be supplied from the saturable reactor, and meansconnected in the supply circuit for the alternating-current windings ofthe saturable reactordisposed to provide a potential drop proportionalto the current flowing in the alternating-current windings to controlthe voltage across and the current fiow in the circuit including thesaturating reactor, the auxiliary control field winding being connectedto be supplied by the rectifier.

2. In a regulating system for a dynamo-electric machine disposed tosupply a load circuit, in combination, an exciter for controlling thefield excitation of the dynamo-electric machine, a main control fieldwinding for the exciter disposed to be directionally energized tocontrol the excitation of the exciter, means responsive to a change incondition of the load circuit supplied by the dynamo-electric machinedisposed for operation to control the directional energization of themain control field winding, an auxiliary control field winding disposedto be energized in one direction only in opposition to a predetermineddirectional .7 7 4 ofthosarlinblooororeactortistgooodtom nmnwnscum a pomdrop proportional a canon ing in the alternating current windings tocontrol y: m a m m the voltage across and m circuit to therebyoontrolthocurrentfluwinuidcircmttheouxil- UNI'IID STATE PA'IIN'IB iarycontrol field winding being connected to be number Rm M 811991164 by1,710,755 Wat m. so, 1929 5am LI: ROY BRADLEY. 2.407.476 Cremsent. 10,1940

